The Different Types of Stars in the Universe

Stars are enormous spheres of ignited gas that light the cosmos, and seed it with the materials for rocky worlds and living beings. They involve many distinct types, sizes and colors that may not be clear enough for the simple human eye.

The amazing light sources are usually classified according to their spectral types. Despite emitting all colors of light, spectral classification only notices the peak of these emissions as a label of the star's surface temperature. By using this system, scientists have managed to discover that blue start, which they like to call the O-type, are defiantly the hottest.

Credit: Michael Shainblum, via Flickr

The coolest starts on the other hand are called M-type and are red. I find this discovery a little bit disturbing since I unwillingly relate the color red to fire and blue to water, but science doesn't care, does it?

This bland categorization is often abandoned and replaced with a more descriptive alternative. As the coolest stars are invariably the smallest, they are called red dwarfs. Conversely, the hottest stars are often called blue giants.

Physical characteristics vary from a star to another and include the surface temperature, luminosity, mass, radius (size), lifetime, prevalence in the cosmos and finally the point in the stellar evolutionary cycle.

1. Yellow Dwarf Stars

Lifetime: 4 - 17 billion years

Evolution: early, middle

Temperature: 5,000 - 7,300 °C

Spectral Types: G, F

Luminosity: 0.6 - 5.0

Radius: 0.96 - 1.4

Mass: 0.8 - 1.4

Prevalence: 10%

This category includes our precious Sun, Alpha Centauri A and Kepler-22. Yes, these are all star names. The designation "yellow dwarf" might be considered a little bit imprecise by some scientists, but these stars do appear yellow when observed through the Earth's atmosphere.

Credit: makelessnoise, via Flick

2. Orange Dwarf Stars

Lifetime: 17 - 73 billion years

Evolution: early, middle

Temperature: 3,500 - 5,000 °C

Spectral Types: K

Luminosity: 0.08 - 0.6

Radius: 0.7 - 0.96

Mass: 0.45 - 0.8

Prevalence: 11%

This category's members are relatively smaller, cooler and have a longer life span. They involve Alpha Centauri B and Epsilon Eridani. These beautiful light sources are main sequence stars like their bigger counterparts, and are fusing hydrogen in their cores.

Credit: R.J. Hall, via Wikimedia Commons

3. Red Dwarf Stars

Lifetime: 73 - 5500 billion years

Evolution: early, middle

Temperature: 1,800 - 3,500 °C

Luminosity: 0.0001 - 0.08

Spectral Types: M

Radius: 0.12 - 0.7

Mass: 0.08 - 0.45

Prevalence: 73%

Red dwarfs, the smallest type of main sequence stars, are barely hot enough to retain the nuclear fusion reactions crucial to the utilization of their hydrogen fuel. They include Bernard's Star, the Gliese 581 and the Proxima Centauri.

The Red dwarf stars are the universe's most common due to their slow rate of fusion and efficient circulation of fuel. Their life spans are thought to exceed 13.8 billion years, a duration no human mind is able to imagine.

Credit: Kilo 66, via Flickr

4. Brown Dwarfs

Lifetime: unknown (long)

Evolution: not evolving

Temperature: 0 - 1,800 °C

Radius: 0.06 - 0.12

Spectral Types: L, T, Y (after M)

Luminosity: ~0.00001

Mass: 0.01 - 0.08

Prevalence: unknown (many)

The relatively small size of Brown dwarfs does not allow them to generate enough heat for hydrogen fusion. These stars are usually of the same size of Jupiter's but 13 times heavier. They are thought to be in a continuing cooling phase which makes them harder to identify.

Credit: European Southern Observatory, via Flickr

5. Blue Giant Stars

Lifetime: 3 - 4,000 million years

Evolution: early, middle

Temperature: 7,300 - 200,000 °C

Spectral Types: O, B, A

Luminosity: 5.0 - 9,000,000

Radius: 1.4 - 250

Mass: 1.4 - 265

Prevalence: 0.7%

These are large stars with a slight blue coloration, although that may be scientifically controversial. Their high temperature allow them to retain their blue color and eventually leads to their transformation into red giants, supergiants or hypergiants due to the non-stop cooling they endure.

Credit: schneidercater, via Flickr

6. Red Giant Stars

Lifetime: 0.1 - 2 billion years

Evolution: late

Temperature: 3,000 - 5,000 °C

Spectral Types: M, K

Luminosity: 100 - 1000

Radius: 20 - 100

Mass: 0.3 - 10

Prevalence: 0.4%

Two examples of this category are Arcturus and Aldebaran. These folks are thought to be in a late evolutionary stage. The accumulation of helium inside them causes an contraction of the core which increases the internal level of temperature. This triggers the hydrogen fusion in the service layers involving the growth in size and luminosity of the star.

Credit: NASA's Marshall Space Flight Center, via Flickr

7. Red Supergiant Stars

Lifetime: 3 - 100 million years

Evolution: late

Temperature: 3,000 - 5,000 ºC

Spectral Types: K, M

Luminosity: 1,000 - 800,000

Radius: 100 - 1650

Mass: 10 - 40

Prevalence: 0.0001%

Due to the contraction of their cores, the Red Supergiant Stars have swelled up. Nevertheless, they are thought to evolve from the blue giants and supergiants with 10-40 solar masses. Two of this kind are Antares and Betelgeuse. With time, these amazing creatures eventually destroy themselves in supernova, probably out of boredom, leaving behind a black hole or a neutron star.

Credit: mike.in.ny, via Flickr

8. White Dwarfs

Lifetime: 1015- 1025 years

Evolution: dead, cooling

Temperature: 4,000 - 150,000 ºC

Spectral Types: D (degenerate)

Luminosity: 0.0001 - 100

Radius: 0.008 - 0.2

Mass: 0.1 - 1.4

Prevalence: 4%

White Dwarfs generate from the remnants of stars less than 10 solar masses, which enter a transformation phase led by Pauli's exclusion principle. They include Van Maanen's star and Sirius B. According to theory, 97% of stars eventually become white dwarfs. These last for trillions of years and end up transforming into black dwarfs after loosing their internal temperature.

Credit: NASA's Marshall Space Flight Center, via Flickr

9. Black Dwarfs

Lifetime: unknown (long)

Evolution: dead

Temperature: < -270 °C

Spectral Types: none

Luminosity: infinitesimal

Radius: 0.008 - 0.2

Mass: 0.1 - 1.4

Prevalence: ~0%

Once a star has become a white dwarf, it will slowly cool to become a black dwarf. The thing that can take trillions of years. As the age of the universe is thought not be even that long, no black dwarf is thought to exist yet.

Credit: NASA's Marshall Space Flight Center, via Flickr

10. Neutron Stars

Lifetime: unknown (long)

Evolution: dead, cooling

Temperature: < 2,000,000 ºC

Spectral Types: D (degenerate)

Luminosity: ~0.000001

Radius: 5 - 15 km

Mass: 1.4 - 3.2

Prevalence: 0.7%

When stars larger than about 10 solar masses exhaust their fuel, their cores dramatically collapse to form neutron stars. The massive collapse intensively throws off the outer layers of the star in a supernova explosion.

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What great pictures and information. It is fascinating, we just spent all of February taking photos of the moon every night for a whole month. I was glad when month over as it was keeping us up all hours of the night trying to get good photos.
What started us on this was buying a new camera that could actually capture the craters on the moon, it was intriguing. Great article thanks for sharing.